ISSN Print: 2327-4336
DOI: 10.4236/gep.2022.108015 Aug. 30, 2022 243 Journal of Geoscience and Environment Protection
Distribution Pattern of Dissolved Inorganic
Nutrients and Phytoplankton Diversity in River Estuary, Kota Kinabalu Sabah, Malaysia
Sujjat Al Azad*, Jiney Liow Fui San, Ejria Saleh
Borneo Marine Research Institute, University Malaysia Sabah, Kota Kinabalu, Malaysia
Abstract
Nutrients are influenced by anthropogenic activities and consequently change the diversity and density of phytoplankton. The spatial distribution of dissolved inorganic nutrients and phytoplankton diversity and density were determined in river estuary, Kota Kinabalu, Sabah, Malaysia. Samples of water and phy- toplankton were collected from six locations of river estuary during the month of May 2019 to October 2019. The highest abundances of 86% diatoms were determined during the study period. This was followed by 13% and 1% of di- noflagellates and Cyanobacteria respectively. The most dominance species of Skeletonema costatum, with density of 1186.69 × 103 cells/L and Thalassiosira sp. (938.01 ×103 cells/L) were recorded from Station 1 (upstream) and Station 5 (mangrove area) respectively. The Chaetoceros sp. (84.25 × 103 cells/L) was the dominated in Station 6 (control site). Station 4 (residential area) accounted the highest diversity of species such as Skeletonema costatum, Thalassiosira sp., Peridinium sp., Gonyaulax sp., and Cylindrotheca sp. with total cell den- sity of 142.98 × 103 cells/L. The high diversity index of 5.2 to 7.09 and even- ness index of 1.81 to 2.87 were determined from this river estuary. Very poor relationship was observed with the cell density and dissolved inorganic nu- trients, phosphate (R2 = 0.2437), ammonium (R2 = 0.301) and nitrate (R2 = 0.406). The diversity and abundance of phytoplankton in this river estuary not only depend on nutrients, but might be associated with other environ- mental factors, tidal fluctuations and rate of discharge of nutrient inputs from surrounding areas. This study suggests that long term monitoring not only the nutrients, but discharges and flushing of nutrient during rainfall and tidal fluctuation together with environmental factors should be considered in or- der to conclude status on the diversity and abundance of phytoplankton in river estuary.
How to cite this paper: Al Azad, S., San, J.
L. F., & Saleh, E. (2022). Distribution Pat- tern of Dissolved Inorganic Nutrients and Phytoplankton Diversity in River Estuary, Kota Kinabalu Sabah, Malaysia. Journal of Geoscience and Environment Protection, 10, 243-258.
https://doi.org/10.4236/gep.2022.108015 Received: June 29, 2022
Accepted: August 27, 2022 Published: August 30, 2022 Copyright © 2022 by author(s) and Scientific Research Publishing Inc.
This work is licensed under the Creative Commons Attribution-NonCommercial International License (CC BY-NC 4.0).
http://creativecommons.org/licenses/by-nc/4.0/
Open Access
DOI: 10.4236/gep.2022.108015 244 Journal of Geoscience and Environment Protection
Keywords
River Estuary, Nutrients, Phytoplankton Abundance, Diversity and Evenness
1. Introduction
Growth and diversity in phytoplankton are controlled by various environmental factors, which are influenced by anthropogenic activities. These could result in massive changes in primary productivity global climate change, ozone depletion and pollution in marine ecosystem (Behrenfeld et al., 2006). The diversity and density of algal species could be obtained from water samples that are possibly helpful to detect early signs of eutrophication (Jafari & Gunale, 2006). River est- uary is influenced by the freshwater and sea water resulted complex ecosystem for the biodiversity. The three major groups of phytoplankton in freshwater ecosystems such as Bacillariophyta (diatoms), Chlorophyta (green algae), and Cyanobacteria. These groups of phytoplankton take massive growth with opti- mum level of phyco-chemical factors such as temperature, dissolved oxygen, pH, dissolved inorganic nutrients (ammonia, nitrogen and phosphate) (Muhammad et al.,2005).
The species diversity, biomass and production of phytoplankton are inter- connected with nutrients (nitrogen and phosphorus) imbalance and availability in aquatic ecosystem. The unhealthy condition of a river is disturbed by anthro- pogenic activities which lead to excess nutrient loading. Thus, invariably chang- ing the physicochemical properties of the water. Increasing of total nitrogen, to- tal dissolved nitrogen, dissolved inorganic nitrogen, nitrate and total phosphorus in the river can speed up eutrophication and cause high phytoplankton abun- dance and diversity. Nitrogen and phosphorus concentration affect the phytop- lankton species composition (Smayda & Reynolds, 2001).
Correlation between phosphorus and abundance of phytoplankton suggests that phosphorus is the controlling factor in phytoplankton growth in the estuary where light is not limiting. Based on the relationship between DO, pH and ab- undance, it is likely that the bloom was caused by rapid in situ growth of phy- toplankton with high nutrients and sufficient light (Gao et al., 2005). Estuaries trap natural and anthropogenic materials by filtering them from surrounding areas to the open sea. Estuarine systems are exposed to cultural eutrophication, resulting in an increase of productivity and large phytoplankton populations.
There are many factors that affect the relative amount of nitrogen in various forms, which are influenced by anthropogenic activities. Phosphorus has been shown to be the production of phytoplankton, while nitrogen is commonly li- miting in marine ecosystems (Cloern, 2001). Phytoplankton communities are not only sensitive to various chemical nutrients but also to environmental fac- tors such as temperature, pH, light etc which affect their occurrence, distribution and diversity.
DOI: 10.4236/gep.2022.108015 245 Journal of Geoscience and Environment Protection In a river system, the current velocity does not allow the planktonic to settle at any place, thus becoming a main limiting factor. Light and nutrients are resources that regulate the quantity, the distribution, and the structure of phytoplankton communities (Diehl et al., 2002). Phytoplankton abundance and diversity are in- fluenced by discharge. The discharges are associated with residence time, chan- nel depth, and dilution rate and affect water transparency and water sedimenta- tion thereby affecting phytoplankton biomass. Information on the distribution of nutrients and its relationship with the phytoplankton communities in riverine estuary around Kota Kinabalu, Sabah is limited. Long term variation on the wa- ter quality of Inanam river estuary are documented (Azad, 2021), but the rela- tionship of nutrients with phytoplankton structure of the river estuary are not established in previous study. Thus present study was conducted on riverine estuary of Darau River that mixed with Likas River at the end mouth of the river flowing towards Seppenger Bay. This estuary significantly increasing of nutrients concentration as runoff water of aquaculture lands and urban development are the major environmental concern at the area for many years. Anthropogenic discharges now a day concern on estuaries quality and considered estuaries as their best option to discharge their waste due to the tide that can dilute and dis- perse undesirable substances. The aim of this study was to determine the spatial distribution of nutrients and phytoplankton diversity and abundance in Kota Kinabalu river estuary.
2. Methodology 2.1. Study Area
The study site is located between latitude 06˚01.189'N and 06˚00.475'N, longitude 116˚07.524'E and 116˚06.335'E. The river estuary is suspected to have high amounts of nutrients concentration due to anthropogenic activities happening at the study area. Six stations were chosen and located based on the source of nutrients as shown in Figure 1. It started with upstream of the estuary (S1), construction de- velopment (S2), near aquaculture farming where water discharged take place (S3), residential area at Kingfisher (S4), at the estuary of mixing point water of Darau and Likas River (S5) and lastly at control station (S6). The detail co-ordinates of sampling station and attribution at each station are shown in Table 1.
2.2. Duration of Sampling
The water samples were taken from May 2019 to October 2019 (six months).
Every month water samples were collected from selected stations in triplicate immediately after the start of low tide.
2.3. Collection of Samples for Water Nutrients Analysis
The water samples were collected from each station by using Van Dorn water sampler and immediately stored into polyethylene bottle. The bottles were la- belled according to station and preserved in cooler box with ice. All of the samples
DOI: 10.4236/gep.2022.108015 246 Journal of Geoscience and Environment Protection Figure 1. Sampling locations (Sources: Google Earth).
Table 1. Coordinates of sampling and attribution at each station.
Stations Coordinates Attributions of Area
1 06˚01.337'N
116˚07.852'E Upstream of the Darau River
2 06˚01.448'N
116˚07.570'E Construction area from Alamesra land development
3 06˚01.741'N
116˚07.313'E Discharges from Aquaculture farm
4 06˚01.369'N
116˚07.109'E Discharges from residential area at Kingfisher
5 06˚00.800'N
116˚06.850'E Mangrove area where Darau and Likas water mix
6 06˚00.740'N
116˚06.488'E Control Site
were brought to Borneo Marine Research Institute Chemical Laboratory for dis- solved inorganic nutrients analysis.
2.4. Collection of Samples for Phytoplankton Cell Density Estimation
Water samples were collected using Van Dorn water sampler within a meter depth and pass through phytoplankton net. Amount of water (liter) pass through net were recorded. Then the water samples were poured into three po- lyethylene bottles and preserved with Lugol’s solution before taken to laboratory for the estimation of cell densities per litre
2.5. Collection of Samples for Phytoplankton Species Diversity
A 20 µm mesh size of phytoplankton net was used and towed horizontally in theDOI: 10.4236/gep.2022.108015 247 Journal of Geoscience and Environment Protection water for a minute. Flow meter was added with plankton net to record the amount of water pass through net. The water samples were transferred into polyethylene bottles and preserved by using Lugol’s iodine for analysis in the lab.
2.6. Analytical Parameters
2.6.1. Determination of Water’s Analytical Parameters (In-situ)
The physical parameters such as Temperature (˚C), Salinity (ppt), pH, Dissolved Oxygen and DO (mg/L) were measured from each six station by using YSI Pro- fesional Plus meter during sampling time.
2.6.2. Laboratory Analysis of Nutrients
The water samples were filtered with 0.45 µm pore-size membrane filter. Con- centration of dissolved inorganic nutrients, such as, phosphate (mg/L), nitrate (mg/L), and ammonium (mg/L) were analyzed with colorimetric method, ac- cording to the procedure described in APHA (2000).
2.6.3. Phytoplankton Species Composition and Cell Density
All the collected phytoplankton species were identification in the laboratory by using Identifying Marine Phytoplankton book by C.R Tomas (1997) published in. The Sedzwick rafter counting chamber was used to number of phytoplankton using a compound microscope. The total number of cells was counted according to the following formula (Stirling, 1985):
( ) ( )
N= A 1000 C× × V F L× ×
N = Number of plankton cells or units per litre of original water A = Total number of plankton counted;
F = Volume of final concentrate of samples in mL L = Volume of original wa- ter in litres;
C = Volume of final concentrate of sample in mL.
2.7. Statistical Analysis
The SPSS Window Program (version 23) was used to find significant difference in concentration nutrients among all stations using one-way Analysis of Variance (1-way ANOVA). Simple linear correlation-regression was established for the re- lationship between nutrient and phytoplankton cell density. One ways ANOVA and significance values were set at p < 0.05 used in this study. The Microsoft Excel was used to calculate the phytoplankton diversity index, species richness and equitability index.
3. Results
3.1. Physico-Chemical Water Parameters
The highest temperature of 31.8 (˚C) in station 2 (construction area) and the lowest temperature of 28.2 (˚C) in station 5 (mangrove area) were recorded during the study period. The lowest 14.1 ppt of salinity was recorded at Station 1
DOI: 10.4236/gep.2022.108015 248 Journal of Geoscience and Environment Protection and the highest salinity of 32.9 ppt was observed at station 6 (control site). Wid- er variations (2 - 7 mg/L) in the concentration of dissolved oxygen concentration were recorded during the sampling period. The values of pH were observed in the range of 6.61 to 8.01 during study period in Kota Kinabalu river estuary (Table 2). No significant differences were (p > 0.05) observed with the physical parameters among the stations except concentration of dissolved oxygen and sa- linity (p < 0.05).
The lowest concentration of phosphate was found in station 6 (0.475 ± 1.042 mg/L). On the other hand, the highest concentration of 0.622 ± 1.161 mg/L of phosphate were recorded at station 2 (Figure 2). No significant differences (p >
1.00) was observed in the phosphate concentrations among the stations.
The highest concentration of ammonium was recorded in Station 1 (2.075 + 0.296 mg/L) followed by Station 2 (1.745 + 0.443 mg/L) and Station 3 (1.652 + 0.443). The lowest concentration of 0.615 + 0.422 mg/L ammonium was ob- served at Station 6 (Figure 3).
Table 2. Physical parameters in each station during study period at Kota Kinabalu river estuary.
Station Temperature (˚C) Salinity (ppt) Dissolved oxygen
(mg/L) pH
Mean Range Mean Range Mean Range Mean Range 1 30.3 29.0 - 31.6 16.5 14.1 - 20.0 2.5 1.4 - 4.3 7.25 6.61 - 8.01 2 31.3 30.3 - 31.8 21.1 18.3 - 23.6 2.7 1.9 - 4.3 7.46 6.65 - 8.27 3 31.1 30.4 - 31.6 23.4 20.6 - 25.0 3.5 2.3 - 4.6 7.59 6.95 - 8.27 4 31.0 30.0 - 32.0 25.9 24.0 - 27.4 4.1 2.7 - 4.9 7.68 6.85 - 8.25 5 30.6 28.2 - 33.0 26.7 19.2 - 30.3 4.6 2.9 - 5.2 7.67 7.01 - 7.83 6 31.3 30.6 - 32.6 31.2 28.0 - 32.9 6.6 4.8 - 7.6 7.93 7.17 - 8.16
Figure 2. The concentration of phosphate (mg/L) at different stations during the study period in the River estuary. There was no significant difference between PO4 among the stations (p > 0.05) although concentration of phosphate was determined different among the stations.
DOI: 10.4236/gep.2022.108015 249 Journal of Geoscience and Environment Protection Figure 3. The concentrations of ammonium (mg/L) at different stations during study pe- riod in River estuary. There was significant difference between NH3 among the stations (p < 0.05). Tukey post hoc test showed that ST6 was significantly difference than ST1, ST2, ST3, ST4 and ST5.
The concentration of nitrate in Station 2 (0.144 ± 0.298 mg/L) was record- ed slightly higher compared to nitrate that was observed at Station 1 (0.141 ± 0.0346 mg/L) while the lowest of 0.042 ± 0.289 mg/L was found at Station 6 (Figure 4).
3.2. Major Group of Phytoplankton
Total 25 types of phytoplankton were identified during the study period (May - October) in this River estuary. The most dominated phytoplankton group in the estuary was the Bacillariophyta accounted 86%, 15 species belongs to this group with total density of 2672.72 × 103 cells/L. The second most dominated eight species of Dinophyta group (13%) with total density 440.30 × 103 cells/L were recorded during sampling period. Only two species of Cyanophyta group was found the with a density of 23.584 × 103 cells/L
3.2.1. Abundance (Cell/L) of Phytoplankton in Each Station
The highest phytoplankton abundances with 142.98 × 103 cells/L was determined in Station 4, followed by the Station 1 (114.06 × 103 cells/L). The lowest of 27.58 × 103 cells/L were observed in Station 6 (Figure 5).
3.2.2. Phytoplankton Species Diversity Index and Evenness Index
The diversity index of phytoplankton among the stations was observed in the range of 5.2 to 7.09. The highest diversity was observed in Station 4. It indicated that the phytoplankton communities in Kota Kinabalu River estuary were fa- vored with environment conditions for their growth and distribution. As for the Evenness Index, Station 4 had the highest value of 2.87 compared to the even- ness value obtained at Station 6 (1.81) assumed that phytoplankton species in Station 6 were not evenly distributed and some other varieties of phytoplankton species are dominating this station than other stations (Figure 6).
DOI: 10.4236/gep.2022.108015 250 Journal of Geoscience and Environment Protection Figure 4. The concentration of nitrate (mg/L) at different stations during study period in Darau River estuary. The concentration of nitrate was significant (p < 0.00) among the stations and showed not many differences.
Figure 5. Total cell density of phytoplankton community (×103 cells/L) in different sta- tions during study period in Kota Kinabalu river estuary.
Figure 6. Species diversity and evenness index of phytoplankton communities at each station in Kota Kinabalu river estuary.
3.3. Relationship of Phytoplankton Abundance (Cell/L) with Dissolved Inorganic Nutrients
Weak correlation was found with the cell density and concentrations of nu-
DOI: 10.4236/gep.2022.108015 251 Journal of Geoscience and Environment Protection trients in River estuary as shown in scattered diagram in Figures 7-9.
4. Discussion
4.1. Physical Parameters
Variations in temperature and values of pH among the stations observed neglig- ible except the concentration of dissolved oxygen and salinity. Physical parame- ters play important roles in the production of phytoplankton productivity if suf- ficient nutrients are available. In an aquatic ecosystem temperature control the overall metabolic activities in a life process, which are influenced by the wind speed, intrusion of freshwater, tide with an effects on the depth of water and of course of atmospheric temperature (Vajravelu et al., 2018). The upstream of this river estuary is dominated by the freshwater flushing from the spring and also from the surrounding human settlement areas. The recorded water temperature
Figure 7. Relationship between Phosphate and phytoplankton cell density in in Kota Ki- nabalu River estuary. The correlation between concentration of phosphate and phytop- lankton cell density was R2 = 0.0243. However slight better correlation was observed with the concentration of ammonium (R2 = 0.301) and nitrate (R2 = 0.406) with phytoplankton cell density.
Figure 8. Relationship between concentration ammonium with phytoplankton cell den- sity in Kota Kinabalu River estuary.
DOI: 10.4236/gep.2022.108015 252 Journal of Geoscience and Environment Protection Figure 9. Relationship between concentration of nitrate with phytoplankton cell density in in Kota Kinabalu River estuary.
are not extremely high (31.8˚C) or low (28.2˚C) indicated not poses any threat in this river estuary. The variations in the concentrations of salinity during study period were remarkable, the highest of 32.9 ppt and the lowest of 14.1 ppt. The lowest values in salinity were recorded in the area (upstream), which are diluted with the freshwater. Increase and decrease in salinity in the brackish water also due to influx of freshwater from surface runoff due to heavy rainfall or tidal var- iations (Srinivasan & Natesan, 2013). However the rainfall data were not rec- orded during the sampling time. On the other hand the highest salinity of 32.9 ppt recorded in the Station 6, the area completely out of freshwater intrusion.
This location is influenced with tidal cycle and relatively weak vertical mixing, leading to an increase in the vertical salinity gradient (Xia et al., 2011) Temper- ature, salinity (Srinivasan & Natesan, 2013) and primary productivity are direct- ly involved in the changes of dissolved oxygen concentration in aquatic ecosys- tem.
The wide variation in the concentrations of dissolved makes this river estuary as complex ecosystem. In general the ranges of 2 to 7 mg/L limit the biodiversity of species in this study area. In general the low concentration of dissolved oxy- gen is the consequences of decaying of organic matter due to rise in temperature and higher microbial activity, which used up oxygen for metabolic process (Eli- ku & Leta, 2018). The lower values in the dissolved oxygen concentrations in the study period might be due to the environmental condition like lowest tidal fluc- tuation, which restricted the intrusion from seawater, which resulted in the lo- wering of salinity and pH (Leidonald et al., 2019). On the other hand the high oxygen values might be the activities of mixing from rainfall and production of phytoplankton biomass, which through the photosynthetic process produces more and more oxygen in River estuary (Aknaf et al., 2017). The variations in the pH values in the range of 6.61 to 8.01 are oblivious due to locations of study areas. In general the lowest values recorded in the stations might be due to the human activities and their settlements around the study areas. The deposition of organic matter and drainage of domestic water might be the major causes of
DOI: 10.4236/gep.2022.108015 253 Journal of Geoscience and Environment Protection changes in the pH values (Dan-kishiya et al., 2013). Excessive uptakes of carbon dioxide in the primary production process limits the acidic condition consequent- ly the higher values in pH are common phenomena in estuary ecosystem. How- ever the tidal fluctuations and the buffering capacity of the seawater control the sudden changes in pH values in the study area (Srinivasan & Natesan, 2013).
4.2. Dissolved Inorganic Nutrients
Phosphorus has been considered the primary limiting nutrient for phytoplank- tonic organisms, although not a limiting nutrient in marine ecosystem. The low- est concentration of phosphate was found in station 6 (0.475 ± 1.042 mg/L). On the other hand, the highest concentration of 0.622 ± 1.161 mg/L of phosphate was recorded at Station 2, but no significantly different among the stations. Phos- phate concentrations around this estuary shows almost similar values as river channel passing through the housing areas, indicating phosphate levels is induced by sewage and wastewater from nearby housing areas. No only human activity, but the distribution of nutrients in the coastal water is influenced by local condi- tions like rainfall, freshwater inflow, and biological activities (Leidonald et al., 2019). On the other hand human activities around the sampling areas are influ- ences by the discharges waste from residential areas as well runoffs and organic wastes (Soon & Ransangan, 2016) around could be factor in controlling phos- phorus in river estuary. The present average phosphate concentration (0.475 - 0.622 mg/L) is comparatively higher the concentration of phosphorus observed in Douala estuary (Fonge et al., 2013) where the concentrations were in the range of 0.03 to 0.04 mg/L. higher values in phosphorus indicating phosphate levels is induced by sewage and wastewater nearby housing areas (Reed et al., 2016). Wa- ter nitrogen is found both as inorganic and organic species and in dissolved and particulate forms. Dissolved inorganic nutrients ammonium was recorded in Sta- tion 1 (2.075 ± 0.296 mg/L) followed by Station 2 (1.745 ± 0.443 mg/L) and Sta- tion 3 (1.652 ± 0.443). The lowest concentration of 0.615 ± 0.422 mg/L ammo- nium was observed at Station 6. Concentration of ammonioum is much higher than range of concentration of 0.02 to 0.38 mg/l that was determined in Sundar- bans mangrove estuarine system of Bangladesh (Rahaman et al., 2013). The Low- er concentrations of ammonium indicate the presence of better quality water.
High ammonium loads can also enhance the development of primary producers.
On the other hand water pH regulates the occurrence of different forms of am- monia in aquatic ecosystem. The higher concentration of ammonium might also be due to wastewater effluents from residential areas and use of fertilizer from agricultural activity nearby land (Lomoljo et al., 2009). Surface run off from surrounding areas and aquaculture activity that uses fertilizers and feed in the fish farm, as well soil erosion might be the factors in the increase of ammonium concentration.
Indeed, the temperature affects the growth rate of bacteria that involved in the nitrification process, with ammonia oxidizers having superior growth rates at
DOI: 10.4236/gep.2022.108015 254 Journal of Geoscience and Environment Protection high temperatures. In fact, the concentration of nitrate and ammonia derived from the upstream areas are not able to accumulate in the estuary as completely flushed out to the open sea with the high tidal fluctuation. The concentration of nitrate in Station 2 (0.144 ± 0.298 mg/L) was recorded slightly higher compared to nitrate that was observed at Station 1 (0.141 ± 0.0346 mg/L) while the lowest of 0.042 ± 0.289 mg/L was found at Station 6 (control station, not influences by human activity. The lower NO3–N concentration of is an indication of little hu- man intervention in the river system. Nitrate concentration was higher due to freshwater influx and discharges of organic and inorganic load due to human induced activities (Kumar et al., 2009). Greater concentration of atmospheric N2
and its continuous mixing in river water through air and surface water interac- tions might be the reason for the irregular fluctuation in NO3–N throughout the sampling periods and tide cycles in the study area. In addition biological oxida- tion of ammonia generate nitrate in aquatic environment with the breakdown of protein. Concentration of nitrate indicates high population pressure and agri- cultural development, as well as fecal pollution (Adedokun et al., 2008) in aqua- tic ecosystem. The concentrations of dissolved inorganic nutrients recorded in the present study observed much lower than the Malaysia NWQS (DOE, 2008) acceptable limits that indicates the healthy ecosystem of river estuary.
4.3. Phytoplankton Community
The abundance and distribution of phytoplankton community largely depends on surrounding physico-chemical water quality parameters, although in river estuary productivity hydrodynamics play crucial roles in changes the nature of the water quality. Thus makes ecosystem of river estuary very complex, all factors are in- terrelated and subsequently contributes in the composition of phytoplankton. A total of 25 species of phytoplankton were identified from present study, on the other hand, 24 genera of phytoplankton were reported from Kota Kinabalu wet- land in undulated areas (Azad & Jinau, 2020) and 21 phytoplankton species are identified from Kudat coastal water (Romin et al., 2021). The environment fac- tors that affect the algal species community and limits the availability of certain types of species are manifolds, like temperature, salinity, Secchi depth (visibili- ty), pH, and dissolved oxygen (Huang et al., 2004). In addition concentrations of nutrients are the major factors together environmental parameters might fa- vor some species to blooms (Hastuti et al., 2018). Although poor relationship between nutrients and availability of phytoplankton were observed, which in- dicates blooming of particular species depends on other environmental para- meters.
The highest phytoplankton abundances with 142.98 × 103 cells/L was deter- mined in Station 4, followed by the Station 1 (114.06 × 103 cells/L). The lowest of 27.58 × 103 cells/L were observed in Station 6 (Figure 5). The highest cell densi- ties in station 4 might be due discharges of nutrients from aquaculture farm lo- cated nearby the location. Aquaculture farm generally uses feed to fed fishes,
DOI: 10.4236/gep.2022.108015 255 Journal of Geoscience and Environment Protection which are rich in nitrogen and phosphorus, together the metabolic waste prod- uct from like faeces and excreta, basically are nitrogenous product also dis- charges in nearby location (Romin et al., 2021). On the hand the lowest cell den- sities was observed in the Station 6, which are limited with the nitrogenous sources in marine environment. Cell density of algal bloom in Kota Belud coast- al area in Sabah was associated with nitrate is limiting factor rather than phos- phate in Kota Belud’s coastal water (Azad et al., 2016). In addition to that heavy rainfall brings nutrients to the study areas via river run-offs during rainy season (Soon & Rangsangan, 2016), although rainfall data was not observed in this study. However poor this study also reported poor relationship between nu- trients and abundance of phytoplankton density (R2 values for phosphate, am- monium and nitrate were 0.2437, 0.301, 0.406 respectively). Composition and abundance of phytoplankton population serve as indicator in changing the nu- trients in marine, which act as important component in the determination of eu- trophication in marine ecosystems (Hastuti et al., 2018). The composition, abun- dance and growth of phytoplankton species are mainly affected by the physical and chemical parameters of the specific marine environment in which they are located (Vajravelu et al., 2018).
The diversity index and species evenness were observed in the range of 5.2 to 7.09 and 1.81 to 2.87 respectively. The observed values were comparatively high- er in present study than that of mean Shannon-Weaver’s diversity index (H') of 2.56 and Pielou evenness index (J') of 0.84 (Romin et al., 2021) and also the di- versity index of 2.35 with evenness index of 0.83 (Fatema et al, 2014). It indi- cated that the phytoplankton communities in Kota Kinabalu River estuary were favored with environment conditions for their growth and distribution.
On the other hand, low diversity index values generally due to low species diver- sity or might also be due to blooming of certain types of species that dominate in ecosystem (Coelho et al., 2007). The relationship between diversity index and evenness are positive and strong. In certain circumstances such as competition, predation, and succession of blooming species changes the diversity index with the alteration in evenness without any change in species richness (Stirling & Wil- sey, 2001). The abundance (Cells/L) of phytoplankton in this study observed higher together with a better diversity index indicate the healthy productive this river estuary. The evenness of the species diversity shows the dominance of cer- tain opportunistic phytoplankton communities, which need further study to look to identify the succession of the species in river estuary. Man-made stres- sors have affected the density of phytoplankton in the study area.
5. Conclusion
Alteration in nutrients and water quality were the major reasons of changes in phytoplankton species diversity and abundances. The household area and aqua- culture activity around this estuary have the highest abundances of nutrients with due to emissions of effluent from the residential sewage nearby during the
DOI: 10.4236/gep.2022.108015 256 Journal of Geoscience and Environment Protection study period. Thus, Kota Kinabalu river estuary might undergo eutrophication due to high input of nutrient loading in the areas such as nitrogen and phos- phorus by anthropogenic activities for examples land degradation, development aquaculture and agriculture practices. Frequent sampling and long term moni- toring on the discharges of nutrients by human induced activity are essentially important to achieve sustainable healthy ecosystem or to avoid eutrophication process in this river estuary.
Conflicts of Interest
The authors declare no conflicts of interest regarding the publication of this pa- per.
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